Chrome was already on a hockey-stick growth curve before the distribution deals started. I remember being in the TGIF where their Founder's Award was announced and one of the questions was "Isn't it a bit premature to give them this award?" (it was 8 months after launch, the Mac version wasn't out yet, and they had about 5% market share) and Larry pointed to the growth chart and said "They've already won, the rest of the world just doesn't know it yet."
I'd actually switched over to Chrome before joining Google, and told all my family to switch, and it was apparent at launch that it was just a better browser. Once you're at the point where your users tell their friends to switch to your product, there's basically nothing your competition can do to stop you other than massively improve their own product, because you're getting large and exponentially-growing amounts of free advertising.
